Method for decreasing the propensity for phase-out of the high molecular weight component of double metal cyanide-catalyzed high secondary hydroxyl polyoxypropylene polyols

ABSTRACT

During polyoxyalkylation in the presence of certain double metal cyanide catalysts, a very high molecular weight hydrophobic fraction, i.e. a &#34;tail&#34;, is produced during preparation of high secondary hydroxyl polyols which is believed to contribute to foam collapse in polyurethane foam formulations. The processing latitude of such foams may be improved by altering the hydrophile/lipophile balance of the high molecular weight tail by oxyalkylating with a mixture of ethylene oxide and higher alkylene oxide during the greatest portion of total oxyalkylation such that essentially pure higher alkylene oxide is present in a terminal portion of oxyalkylation not exceeding 15 weight percent of total polyol weight.

This is a division of application Ser. No. 08/805,788, filed Feb. 25,1997 which is now U.S. Pat. No. 5,958,994.

TECHNICAL FIELD

The present invention pertains to polyoxypropylene polyols. Moreparticularly, the present invention pertains to high secondaryhydroxyl-terminated polyoxypropylene polyols prepared by the doublemetal cyanide-catalyzed oxypropylation of a suitably hydric initiator,and to a method of altering the structure of a high molecular weightcomponent of such polyols so as to decrease their propensity towardphase-out in polymerizing polymer systems.

BACKGROUND ART

Polyoxyalkylene polyether polyols are now a mainstay of the polyurethaneindustry, and have a myriad of other uses outside of polyurethanes aswell, e.g. as surfactants, fat substitutes, and the like. While higheralkylene oxides such as butylene oxides and higher α-olefin oxides areused in the preparation of some polyether polyols, particularly thoseused as surfactants, the majority of polyether polyols produced todayare prepared by polyoxyalkylation with ethylene oxide, propylene oxide,or mixtures thereof, in either block, random, or block random fashion.Oxyalkylation has been generally conducted in the presence of a basicmetal catalyst such as sodium hydroxide, potassium hydroxide, or analkali metal alkoxide. Such catalysts are relatively inexpensive, andreadily available.

During base catalyzed oxyalkylation with propylene oxide, however, acompeting rearrangement of propylene oxide into allyl alcohol during thecourse of the reaction continually introduces a monohydroxylfunctionalmolecule, which itself is capable of being oxyalkylated. Thus, as thereaction progresses, more and more monofunctional species and theiroligomeric oxyalkylated products accumulate, reducing the averagefunctionality of di- and poly-functional polyols and broadening theirmolecular weight distribution as well. Discussion of the mechanism ofthis rearrangement is discussed in BLOCK AND GRAFT POLYMERIZATION, v. 2,Ceresa Ed., John Wiley & Sons, on pages 17-21. The monol content inconventionally base catalyzed polyoxypropylene polyols is ascertained bymeasuring unsaturation content, for example by ASTM D-2849-69, "TestingUrethane Foam Polyol Raw Materials", and is generally in the range of0.08 meq/g to 0.10 meq/g or higher.

For example, in the production of a 2000 Da (Dalton) equivalent weightpolyoxypropylene diol, it is not uncommon for the mol percentage ofunsaturated monofunctional species to approach 30-40%, lowering thetheoretical functionality of 2 to a functionality in the range of 1.6 to1.7. It is believed by some that the high monofunctionality of thepolyols produced through base catalysis places a severe limitation onthe ultimate molecular weight of polymers obtained therefrom due to theability of the monofunctional species to act as chain terminators duringpolymerization. Moreover, the presence of the unsaturated allyl groupmay sometimes have deleterious effects associated with the reaction ofthe allylic double bond or its oxidation into a variety of oxidationproducts. Thus, attempts have been made to reduce the amount ofmonofunctional species as reflected by measuring the unsaturationcontent of polyether polyols.

For example, use of rubidium and cesium hydroxide as oxyalkylationcatalysts in place of the normally used sodium and potassium hydroxideshas been found to lower the degree of unsaturation as disclosed in U.S.Pat. No. 3,393,243. However, the decrease is somewhat modest and thecatalysts are far more expensive. Use of barium and strontium hydroxidesand oxides is disclosed in U.S. Pat. Nos. 5,010,187 and 5,114,619. Inaddition to being far more expensive than alkali metal hydroxides, bothbarium and strontium, particularly the latter, are relatively toxic.Thus, little if any commercialization of such processes have been made.The use of metal naphthenates, optionally in conjunction with tertiaryamine co-catalysts, has been shown to be capable of producingpolyoxyalkylene polyols of modest molecular weights with unsaturationsas low as 0.02 to 0.04 meq/g. See, e.g., U.S. Pat. No. 4,282,387.However, these polyols still contain an appreciable monofunctionalcontent, and have been shown to be little different their behavior inpolymer systems from higher unsaturation polyols produced throughconventional base catalysis.

In the decade of the 1960's, non-stoichiometric double metal cyanidecatalysts, i.e. the glyme adduct of zinc hexacyanocobaltate, were shownto be efficient catalysts for polyoxyalkylations and various otherreactions as well. In addition to possessing relatively high rates ofreaction, the double metal cyanide catalysts were found to be capable ofproducing polyols with relatively low unsaturation content, withunsaturations in the range of 0.018 to 0.020 easily obtainable. However,due to the greater cost of these catalysts, coupled with the difficultyof removing them from the finished polyol product, commercialization ofsuch systems did not materialize. Interest in DMC catalysts resurfacedin the 1980's, and improvements in the catalytic activity coupled withnew and improved methods of removal from the finished product resultedin commercialization of DMC catalyzed polyol production for a shortperiod of time. The polyols produced by these improved DMC catalystsexhibited unsaturation in the range of 0.015 to 0.018 meq/g.

Recent further improvements in the activity of DMC catalysts by the ARCOChemical Company has once again resulted in commercialization of DMCcatalyzed polyoxyalkylene polyols under the tradename ACCLAIM™ polyols.The catalytic activity of the new DMC catalysts has been improved tosuch an extent that frequently the rate of polyoxyalkylation is limitedby the ability to transfer heat from the polymerization reactor ratherthan by the activity of the catalyst. The decreased processing timeincreases the cost/benefit ratio of the catalysts, encouraging theircommercial use.

The availability of ultra-low unsaturation polyoxyalkylene polyols hasnot proven to be the panacea expected. The polyols have not proven to bedrop-in replacements for conventionally catalyzed polyether polyols, andin fact, polyether polyols produced by DMC catalysts having unsaturationin the range of 0.003 to 0.010 meq/g have surprisingly been found to bequantitatively different from other, "low" unsaturation polyoxyalkylenepolyols, even those produced by prior generation DMC catalysis. Althougha portion of the differences between ultra-low unsaturation polyetherpolyols, low unsaturation polyols, and conventional polyoxyalkylenepolyols can be attributed to the differences in functionality, molecularweight distribution, and lack of monofunctional species, the manner inwhich each of these properties affects both polyurethane formulation andthe polyurethanes obtained therefrom is not fully understood. In manycases, for example, improved polyurethane products could indeed beproduced, but only by unusual and non-obvious changes in formulation andprocessing parameters. The anomalous behavior of ultra-low unsaturationpolyoxyalkylene polyols and the reasons therefore are still beinginvestigated. One example of this anomalous behavior is the collapse ofpolyurethane foam systems which employ high secondary hydroxyl contentultra-low unsaturation polyoxypropylene polyols, while similar systemsemploying conventional polyols produced good foams.

It has been recently discovered that polyoxypropylations with somedouble metal cyanide catalyst systems, particularly those capable ofproducing ultra-low unsaturation polyether polyols, also produce a verysmall but significant quantity of very high molecular weight product.The existence of this very high molecular weight "tail" was notexpected, as double metal cyanide catalysts are known to producepolyether polyols of very low polydispersity, with polydispersities onthe order of 1.07 to 1.20 being routinely achieved. This polydispersityis far lower than those obtainable with alkali metal catalysis and othermethods of catalyzing the oxyalkylation, and gel permeationchromatography shows a relatively tight and narrow distribution ofmolecular weights.

Upon careful analysis of larger quantities of polyol, concentrating onthe portion eluting significantly prior to the main product peak, a veryhigh molecular weight component was surprisingly discovered. Carefulanalysis of this high molecular weight "tail" indicates that it iscomposed mostly of polyoxypropylene polyols having molecular weights inexcess of 100,000 Da. Once being appraised of the existence of the highmolecular weight tail, the reasons for its production may behypothesized. Without wishing to be bound to any particular theory,Applicants believe that the non-stoichiometric double metal cyanidecatalysts contain a very minor portion of catalytic sites for which thetransfer coefficient is exceptionally small. While the vast majority ofcatalytic sites exhibit rapid substrate transfer, resulting in a verynarrow and tight molecular weight band, a small fraction of thecatalytic sites may exhibit virtually no transfer whatsoever, thusproducing at those sites a higher and higher molecular weight product.Applicants believe that this high molecular weight tail may be one facetof the explanation of the anomalous behavior of DMC catalyzed ultra-lowunsaturation polyether polyols in some applications.

One example is the production of polyurethane foam from high secondaryhydroxyl polyoxypropylene polyols. It is known that the hydrophilicityand hydrophobicity of polyethers is affected by molecular weight.Further, it is believed that the high molecular weight species isvirtually all polyoxypropylene homopolymer. Thus, while ethylene glycol,oligomeric ethylene glycols, and even high molecular weightpolyoxyethylene glycols are all hydrophilic to some degree,polyoxypropylene glycols are hydrophilic only up to a molecular weightof approximately 500 Da, following which they become increasinglyhydrophobic. This phenomenon has been utilized in the preparation ofpolyoxyethylene/polyoxypropylene block copolymers useful as nonionicblock surfactants.

In the production of polyurethane foam, the foam chemistry is verycritical. For example, acceptable polyurethane foams are rarely obtainedwhen incompatible polyols are utilized in the foam formulation. Anincompatible polyols is one which is insoluble or of limited solubilityin the unreacted or partially reacted foam forming ingredients. This isone reason polyethylene glycols are rarely used in foam formulationsexcept in most minor amounts, as the polyoxyethylene polyols aregenerally of very limited solubility in the reactive components. On theother hand, polyoxypropylene polyols of modest molecular weight tend tobe compatible in this respect. During the condensation polymerizationwhich takes place during foam formation, the growing polyurethane and/orpolyurethane/urea polymers increasingly incorporate relatively polarurethane and urea groups, thus altering the hydrophile/lipophile balanceof the growing polymer chain. It is believed that foam collapse occursin foam formulations employing high secondary hydroxyl, ultra-lowunsaturation DMC catalyzed polyoxypropylene polyols having a highmolecular weight tail, because the high molecular weight tail, beingexceptionally hydrophobic, tends to phase out, or separate from thegrowing polymer matrix, disrupting cell walls and eventually causingfoam collapse.

Elimination of the high molecular weight tail from polyoxyalkylenepolyols containing such a tail by removing the latter is virtuallyimpossible, as in general, the polyoxyalkylene polyol products are offar too high a molecular weight for efficient distillation, even withmethods such as falling film evaporation or wiped film evaporation, andmoreover, such evaporative processes are relatively expensive, addingunwanted cost to the polyether product. If a method of precipitating thehigh molecular weight tail could be found, the high molecular weightportion could be filtered out. However, filtration of relatively viscouspolyols is a long and expensive process. Again, the cost benefit ratiowould dictate against the use of such a method even if such a methodwere available.

It would be desirable to produce low and ultra-low unsaturation, highmolecular weight polyoxyalkylene polyols with high secondary hydroxylcontent wherein the phase-out of the high molecular weight tail duringpolyurethane formation is markedly decreased or eliminated. It wouldfurther be desirable to produce a polyether polyol product wherein thehigh molecular weight tail is less hydrophobic than a polyoxypropylenehomopolymer.

SUMMARY OF THE INVENTION

It has now been surprisingly discovered that the propensity towardphase-out of the high molecular weight tail of high secondary hydroxylpolyoxyalkylene polyols prepared from higher alkylene oxides in thepresence of double metal cyanide complex (DMC) catalysts may besubstantially decreased if, during at least the first 80% of polyolproduction, a mixture of higher alkylene oxide and ethylene oxide, forexample but not by limitation, a mixture containing ethylene oxide in anamount from about 0.5 to 15 weight percent, is utilized as the alkyleneoxide mixture.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The claimed polyoxyalkylene polyols and method for their production areboth limited to polyoxyalkylene polyols prepared from at least onehigher alkylene oxide and which have a high molecular weight tail, i.e.a high molecular weight fraction having a molecular weight higher thanabout 100,000 Da. By "higher alkylene oxide" is meant propylene oxide,butylene oxide, or other alkylene oxide which is capable ofpolymerization to form hydrophobic species. Ethylene oxide, for example,does not form hydrophobic species. Moreover, homopolymerization ofethylene oxide is generally conducted with basic catalysts, even to veryhigh molecular weights, as ethylene oxide is not subject torearrangement as are propylene oxide and other higher alkylene oxides.Furthermore, ethylene oxide in general, cannot be homopolymerized by DMCcatalysts, as such polymerizations generally produce somewhatintractable mixtures containing a variety of polymeric products whoseidentity has not been ascertained, but which are believed to containultra-high molecular weight polyoxyethylene waxes in conjunction withlower molecular weight and oligomeric polyoxyethylene glycols.Preferably, the higher alkylene oxide is propylene oxide, or propyleneoxide in admixture with one or more butylene oxides or oxetane.

The presence of the high molecular weight tail can be verified by gelpermeation chromatography of a polyol sample. The high molecular weighttail will have a molecular weight in excess of 80,000 Da for polyolswith average equivalents weights of from about 1,000 Da to about 15,000Da. Most often, the high molecular weight tail will have a molecularweight of c.a. 100,000 Da or higher for such polyols. The terms "averagemolecular weight" and "equivalent weight" refer to number averagemolecular weight and number average equivalent weight herein unlessindicated otherwise.

While gel permeation chromatography is a useful method of detecting thepresence of the high molecular weight tail, its presence can be moreeasily and rapidly detected qualitatively by employing a high secondaryhydroxyl polyol in a highly stressed foam formulation. For example, asuitable highly stressed foam formulation is given in Example 1 of thesubject invention. This foam formulation employs ingredients typical offoam formulations employing high secondary hydroxyl polyols, i.e.conventional surfactants, catalysts, etc. High secondary hydroxylpolyols are generally homopolymeric polyols produced from all propyleneoxide. If such a polyol is produced with an ultra-low unsaturation DMCcatalyst, the presence of significant amounts of high molecular weighttail will be shown by the foam's collapse. Thus, either gel permeationchromatography or other suitable method of analyzing the polyol in termsof the molecular weights of its various fractions, or the collapsingfoam test may be used to detect the presence of the high molecularweight tail.

To reduce the effect of the high molecular weight tail in accordancewith the subject invention, it has been found necessary to conduct theDMC catalyzed oxyalkylation in the presence of ethylene oxide for asubstantial part of the oxyalkylation. If ethylene oxide is presentduring the entire oxyalkylation, then a polyol of higher primaryhydroxyl content is obtained, which is generally not desired. If theoxyalkylation is conducted in the presence of ethylene oxide for lessthan about 80% of the total oxyalkylation, i.e. if the last 20% or moreof the oxyalkylation is conducted with all propylene oxide or otherhigher alkylene oxide, then it is found that the solubility parameter ofthe high molecular weight tail is such that phase-out is likely to occurduring polyurethane formation.

If, however, less than 20% of the total oxyalkylation, and inparticular, less than 20%, preferably less than 15%, and most preferably12% or less of the final portion of the total oxyalkylation is conductedwith propylene oxide, then the hydrophile/lipophile balance of the highmolecular weight tail will be such so as to minimize phase-out from agrowing polyurethane or polyurethane/urea chain. This is evidenced byfoam stability rather than foam collapse. Without wishing to be bound toany particular theory, it is believed that even the relatively smallpercentage of ethylene oxide present causes a portion of the alkyleneoxide residues of the high molecular weight tail to be ethyleneoxide-derived, lowering the hydrophobicity of this portion of theproduct significantly without being present in the desired lowermolecular weight fraction to an extent which prohibits its use inpolyurethane foam systems.

Not all DMC catalysts which are capable of producing ultra-lowunsaturation polyether polyols will demonstrate the formation of a highmolecular weight tail. At times, even the same DMC catalyst in slightlydifferent physical forms may produce polyols with differing highmolecular weight tails or even lack of high molecular weight tail. Thus,for any given polyol it is first necessary to determine whether a highmolecular weight tail having an undesirable hydrophile/lipophile balanceis obtained during normal polyoxyalkylation. To determine this, a highsecondary hydroxyl content polyoxyalkylene polyol is prepared byoxyalkylation without ethylene oxide being present. For example, but notby way of limitation, a di- to octa-hydric initiator may be oxyalkylatedwith propylene oxide in the presence of the DMC catalyst to produce forexample, a polyoxypropylene polyol having an equivalent weight of about6,000. This polyol product may be examined by GPC and/or by thecollapsing foam test to ascertain whether the high molecular weight tailis present, and if so, whether modification of its hydrophobicity shouldbe made in order to avoid foam collapse. If a significant high molecularweight tail is found to be present, then the effect of this highmolecular weight tail on developing foam can be reduced by preparing anotherwise similar polyol, but employing from about 0.5 to about 15%ethylene oxide during a substantial part of the oxyalkylation, forexample, for substantially all of the initial oxyalkylation up to thepoint where a final oxypropylene or other higher alkylene oxide derivedterminal block is necessary to produce a high secondary hydroxyl cap.

For example, it has been found highly advantageous to conduct theinitial polyoxyalkylation with propylene oxide up to an equivalentweight of about 500. This initial polyoxyalkylation may take place inthe presence of a DMC catalyst, or a conventional catalyst such as, butnot limited to, the catalytic systems previously described. If thisinitial oxyalkylation takes place in the presence of a conventionalbasic catalyst, then the oligomeric polyol must be treated to removecatalyst, otherwise the DMC catalyst may be inactivated. Followingoligomeric polyoxyalkylation, oxyalkylation is continued with a mixtureof ethylene oxide and propylene oxide containing less than 15% ethyleneoxide, more preferably less than 10% ethylene oxide, and yet morepreferably ethylene oxide in an amount from about 1 weight percent toabout 5 weight percent up to the point where 85% or thereabouts of thefinal polyol target weight has developed, following which thepolymerization is conducted with all propylene oxide. It is mostpreferable that no more than the last 15% of the oxyalkylation beconducted with higher alkylene oxide, preferably, no more than 12%, andmost preferably about 6.5% or less. However, if less than about 5% ofthe final oxyalkylation is conducted with propylene oxide or otherhigher alkylene oxide, then the polyoxyalkylene polyol product will havea higher primary hydroxyl content, and thus will not be a high secondaryhydroxyl polyol as required by the claims.

It must be understood that when the final oxyalkylation is conductedwith all propylene oxide, the actual alkylene oxide mixture will stillcontain a small amount of ethylene oxide. Thus, by the finaloxyalkylation being conducted with higher alkylene oxide alone is meantthat the content of ethylene oxide during this phase of oxyalkylation issuch that the secondary hydroxyl content of the finished product issubstantially the same as would be prepared in the total absence of apurposefully added co-feed of ethylene oxide. In other words, the finalalkylene oxide feed is substantially all propylene oxide or other higheralkylene oxide. Such oxypropylation results in formation of asubstantially homopolyoxypropylene cap.

Initiators suitable for use in preparing the polyoxyalkylene polyols ofthe subject invention include those conventionally used in polyurethanepolyol and nonionic surfactant production. Examples include, but are notlimited to, ethylene glycol, diethylene glycol, triethylene glycol,propylene glycol, dipropylene glycol, tripropylene glycol,1,3-propanediol, 1,4-butanediol, 1,6-hexanediol; trihydric initiatorssuch as glycerine, trimethylolpropane, trimethylolethane; tetrahydricinitiators such as pentaerthyritol; hexahydric initiators such assorbitol, and other saccarides; and octahydric initiators such assucrose. Other initiators such as oxyalkylated amines. oxyalkylateddiamines, and the like, for example tetrakis[2-hydroxyalkyl]ethylenediamines, and various alkylated anilines and methylenedianilines may beused. Oligomeric oxyalkylation products of all of the above may also beused, and in many cases are preferred. For use as surfactants,monofunctional initiators such as methanol, butanol, n-octanol,nonylphenol, and the like may be used. However, in such cases, thepresence of high molecular weight tail must be assessed.

It has been rather surprisingly found that the same DMC catalyst mayproduce a high molecular weight tail when used in one form whereas itwill not when used in another form. For example, when charged to thereactor in paste form, a high molecular weight tail may be obtainedwhereas the same catalyst in powder form may not produce a tail and viceversa. It is possible that in some instances the length and/or nature ofstorage of the catalyst may impact its tail-producing propensity. Insuch cases, if a given form of catalyst is known to produce a highmolecular weight tail after storage for a known or unknown period oftime, then it may be desired to employ the subject invention processwith all high secondary hydroxyl polyols produced using the catalyst, orto use the subject invention process with all polyol production wherestorage exceeds a particular storage time. By the term "in need thereof"it respect to mitigating the effect of a high molecular weight tail inpolyol production is meant polyol production where without use of thesubject invention, a substantially all-higher alkylene oxide, i.e.propylene oxide hydrophobic tail is known to be produced, or whoseproduction is anticipated.

Examples of DMC catalysts which may be employed to produce low orultra-low polyether polyols which should be examined for the presence ofa high molecular weight tail include those disclosed in U.S. Pat. Nos.5,100,997; 5,158,922; 5,470,812; and 5,482,908, which are hereinincorporated by reference. The DMC catalysts must be capable ofpreparing a polyoxyalkylene polyol with an amount of monol, as reflectedby the allylic unsaturation present, of less than 0.015 meq/g,preferably less than 0.012 meq/g, more preferably less than 0.010 meq/g,and most preferably about 0.003 to 0.007 meq/g or less. Polyols havingunsaturations in the range of 0.012 to 0.015 meq/g may be termed "lowunsaturation polyols." Polyols with unsaturations of less than 0.010meq/g are termed "ultra-low unsaturation polyols." It has beensurprisingly discovered that the behavior of ultra-low unsaturationpolyols is quantitatively different and often unpredictable as comparedto low unsaturation polyols.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

Critical Foam Formulation Testing

The presence or absence of a deleterious high molecular weight tail in apolyoxypropylene polyol used in polyurethane foams may be qualitativelyassessed by employing the polyol in a highly stressed hand-mixed foamformulation. In this test, a foam prepared from a given polyol isreported as "settled" if the foam surface appears convex after blow-offand is reported as collapsed if the foam surface is concave afterblow-off. The amount of collapse can be reported in a relativelyquantitative manner by calculating the percentage change in across-sectional area taken across the foam. The foam formulation is asfollows: polyol, 100 parts; water, 6.5 parts; methylene chloride, 15parts; Niax® A-1 amine-type catalyst, 0.03 parts; T-9 tin catalyst, 0.4parts; L-550 silicone surfactant, 0.5 parts. The foam is reacted with amixture of 2,4- and 2,6-toluenediisocyanate at an index of 110. The foammay be conveniently poured into a standard 1 cubic foot cake box, or astandard 1 gallon ice cream container. In this formulation,conventionally prepared, i.e. base catalyzed polyols having highsecondary hydroxyl cause the foam to settle approximately 5-10%, whereaspolyols prepared from DMC catalysts exhibiting high molecular weighttails as disclosed in the present invention, cause the foam to collapseby approximately 40-70%. A change of greater than 40% is consideredcollapse.

Analytical Procedure for Determining High Molecular Weight Tail

The analytical procedure useful for obtaining the quantity of highmolecular weight tail in a given DMC catalyzed polyol is a conventionalHPLC technique, which can easily be developed by one skilled in the art.The molecular weight of the high molecular weigh, fraction may beestimated by comparing its elution time in the GPC column with that of apolystyrene standard of appropriate molecular weight. For example, apolystyrene of 100,000 molecular weight has been found appropriate formost analyses. As is well known, high molecular weight fractions elutefrom a GPC column more rapidly than lower molecular weight fractions,and to aid in maintaining a stable baseline, it is appropriate followingthe elution of the high molecular weight fraction, to divert theremainder of the HPLC eluate to waste, rather than allowing it to passthrough the detector, overloading the latter. Although many suitabledetectors may be utilized, a convenient detector is an evaporative lightscattering detector (ELSD) such as those commercially available.

In the preferred analysis method, a Jordi Gel DVB 10³ Angstrom column,10×250 mm, 5 micron particle size, is employed with a mobile phase whichconsists of tetrahydrofuran. The detector used is a Varex Model IIAevaporative light scattering detector. Polystyrene stock solutions aremade from 591,000 Da molecular weight polystyrene by appropriatedilution with tetrahydrofuran, to form standards containing 2, 5, and 10mg/L of polystyrene. A molecular weight calibration standard wasprepared from 100,000 Da molecular weight polystyrene in a similarmanner.

Samples were prepared by weighing 0.1 gram of polyether into a 1 ouncebottle, and adding tetrahydrofuran to the sample to bring the totalweight of sample and tetrahydrofuran to 10.0 grams. Samples of the 2, 5,and 10 mg/L polystyrene solutions and 100,000 molecular weightcalibration solution are sequentially injected into the GPC column.Duplicates of each polyol sample solution are then injected, followingby a reinjection of the various polystyrene standards. The peak areasfor the polystyrene standards are electronically integrated, and theelectronically integrated peaks for the two sets of each candidatepolyol are electronically integrated and averaged. Concentration of thehigh molecular weight tail in ppm is then performed by standard datamanipulation techniques.

Polyol Preparation

In the examples which follow, a series of polyols were made by the samegeneral procedure. The starter, or initiator, is a KOH base-catalyzedoxypropylation product of glycerine having a molecular weight of about690 to 720, which has been refined by conventional techniques to removeresidual traces of KOH. The catalysts utilized are ultra-lowunsaturation-producing DMC catalysts as disclosed in U.S. Pat. Nos.5,470,813 and 5,482,908. The particular method of catalyst preparationis not part of, nor relevant to the subject invention. All catalysts arenon-stoichiometric, substantially amorphous, zinc hexacyanocobaltateT-butanol complexes, with or without additional complexing agents.Detailed preparation of suitable catalysts may be referred to thepreceding patents, which are herein incorporated by reference.

An amount of starter is added to a stainless steel reactor, andsufficient catalyst mixed with the starter to yield either 25 ppm or 30ppm, respectively, of catalyst on a solids basis in the finalpolyoxyalkylene product. The catalyst is activated by adding propyleneoxide to the reactor and carefully observing the pressure in thereactor, as disclosed in the preceding U.S. patents. A drop in pressureindicates that the catalyst has been activated. Following activation,propylene oxide and ethylene oxide feed rates are increased to the finalfeed rates in a period of about 30 or more minutes, the co-feed in theseexamples being approximately 83/17 propylene oxide/ethylene oxide. Afterfeeding in the total amount of propylene oxide/ethylene oxide co-feed,the final addition of substantially all propylene oxide is fed toproduce a homopolyoxypropylene cap of the desired percentage weight. Thetotal oxide feed time is approximately 6.5 hours. Following addition ofpropylene oxide, the reactor is held at about 130° C. for 90 minutes toconsume unreacted propylene oxide. The polyol is then cooled to 80° C.and transferred to a holding vessel, following which anti-oxidant may beadded if desired, and the polyol filtered to remove large particles.

In the following examples, three catalysts were generally utilized,catalyst #1 is a powdered DMC catalyst utilized at a concentration of 25ppm; catalyst #2 is a paste DMC catalyst utilized at a concentration of25 ppm; while catalyst #3 is chemically different from catalysts 1 and 2and is utilized at a concentration of 30 ppm.

COMPARATIVE EXAMPLES C1 to C3

Three polyols were prepared substantially as in the procedure disclosedpreviously, however, in place of the homopolyoxypropylene cap, theentire oxyalkylation was conducted with an 83/17 ratio of propyleneoxide/ethylene oxide. In Comparative Example C1, no heel was utilized,whereas in Comparative Examples C2 and C3, 8% heels, i.e. approximately8% of the reactor volume contained polyol from the previous batch, wasutilized. Each of these comparative polyols, having no polyoxypropylenecap, were found to pass the highly stressed foam test. The results areindicated in Table 1.

EXAMPLES 4-13

These Examples were performed as in the preceding Examples, with varyingamounts of propylene oxide cap, and with varying amounts and types ofcatalysts. Some reactions were performed with the reactor containing aheel of a prior reaction. The presence or absence of a heel had nosignificant effect on the amount of high molecular weight tail or theevaluation of foams prepared from the polyol in the stressed foam test.It is noteworthy that in all of the Examples and Comparative Examplesherein, a high molecular weight tail was detected in amounts rangingfrom about 167 ppm to 686 ppm. The results are printed in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                           High MW Tail                                                                         Initial                                         Example                                                                            PO Cap, Wt %                                                                         Catalyst, Amount (type)                                                                  Results, ppm                                                                         Foam Results.sup.1                              __________________________________________________________________________    C1   0.0%   25 ppm (2) 281    Pass, 20%                                       C2   0.0%   25 ppm (2) 238    Pass, 6%                                        C3   0.0%   30 ppm (3) 266    Pass, 9%                                        4    25.0%  25 ppm (1) 225    Fail, 50%.sup.2                                 5    25.0%  25 ppm (2) --     Fail, 70%                                       6    25.0%  30 ppm (3) 228    Pass, 14%                                       7    12.5%  25 ppm (1) 686    Fail, 46%                                       8    12.5%  25 ppm (2) 341    Fail, 58%                                       9    12.5%  30 ppm (3) 167    Pass, 9%                                        10   6.5%   25 ppm (1) 240    Pass, 20%                                       11   6.5%   25 ppm (2) 220    Pass, 11%                                       12   6.5%   25 ppm (2) 255    Pass, 7%                                        13   6.5%   25 ppm (3) 228    Pass, 15%                                       __________________________________________________________________________     .sup.1 Using the highly stressed foam formulation                             .sup.2 Percent Settle, if greater than -40% the foam collapsed           

As can be seen from Table 1, preparation of polyoxyalkylene polyolshaving high secondary hydroxyl group content by DMC catalysis does notalways result in polyols which exhibit foam collapse in the highlystressed foam test. This may be due to a lesser content of the highmolecular weight tail in parts per million, or to the nature of the highmolecular weight tail itself, i.e. its relative hydrophobicity orhydrophilicity, or both. As the highly stressed foam test is somewhatqualitative, it is quite possible that other stressed formulations mayshow collapse where the present formulation does not. Polyols with nohomopolyoxypropylene cap uniformly pass the highly stressed foam test,despite having moderate levels or high molecular weight tail, i.e. 238to 281 ppm. With a 6.5% homopolyoxypropylene cap, the amount of highmolecular weight tail was substantially the same, i.e. from 220 to 255ppm, and again, all polyols passed the highly stressed foam test.

In Examples 7-9, with a homopolyoxypropylene cap of 12.5 weight percent,polyols prepared from the Type 1 and Type 2 catalysts at 25 ppmconcentration both failed the test, with substantial foam collapse.Moreover, the amount of high molecular weight tail in both theseexamples is relatively high, 686 ppm and 341 ppm.

With a higher propylene oxide cap, 25%, as illustrated in Examples 4-6,again, the polyol prepared from the Type 3 catalyst passed the highlystressed foam test, although having a high molecular weight tail portionof 228 ppm. Examples 4 and 5, however, failed the test with substantialfoam collapse, despite the fact that the amount of high molecular weighttail itself, 225 ppm, is not substantially different from those otherfoams that passed the test. The fact that the amount of high molecularweight tail itself can be the same, and yet some foams pass the testwhile some fail, indicates that it is the nature of the high molecularweight tail, which is responsible for foam collapse in these cases, andnot the amount. Ideally, it would be desirable to produce a polyol withno high molecular weight tail, however, viewing the results, it appearsthat this desired goal will have to wait for the development of newcatalysts and/or new processes.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of the inventionas set forth herein.

What is claimed is:
 1. A high secondary hydroxyl group-contentpolyoxypropylene polyol prepared by the double metal cyanide catalyzedoxypropylation of a suitably hydric initiator having a cap comprisingpolymerized propylene oxide moieties, said polyol comprising in mostmajor part a polyoxypropylene polyol having an average equivalent weightof from about 1000 Da to about 15,000 Da and a random, internaloxyethylene content of from about 0.5 weight percent to about 15 weightpercent and a polyoxyalkylene tail having an average molecular weightgreater than about 80,000 Da, said tail containing oxypropylene andoxyethylene moieties, said polyoxypropylene polyol having ahomopolyoxypropylene cap which constitutes less than about 15 percent byweight of said polyol.
 2. The polyoxypropylene polyol of claim 1 has arandom oxyethylene content of from about 0.5 weight percent to about 12weight percent based on he weight of said polyoxypropylene polyol. 3.The polyoxypropylene polyol of claim 1 wherein said polyoxypropylenepolyol has a random oxyethylene content of about 12 weight percent basedon the weight of said polyoxypropylene polyol.
 4. The polyoxypropylenepolyol of claim 1 wherein said polyoxypropylene polyol has a randomoxyethylene content of less than about 12 weight percent based on theweight of said polyoxypropylene polyol and wherein saidhomopolyoxypropylene cap comprises no more than about 12.5 weightpercent based on the weight of said polyoxypropylene polyol.
 5. Thepolyoxypropylene polyol of claim 1 wherein said polyoxypropylene polyolhas a random oxyethylene content of less than about 12 weight percentbased on the weight of said polyoxypropylene polyol and wherein saidhomopolyoxypropylene cap comprises no more than about 8 weight percentbased on the weight of said polyoxypropylene polyol.
 6. Thepolyoxypropylene polyol of claim 1 wherein at least a portion of saidtail of said polyoxypropylene polyol has a molecular weight of about100,000 Da or more.
 7. The polyoxypropylene polyol of claim 1 whereinsaid oxyethylene moieties are introduced into said polyoxypropylenepolyol by oxyalkylating with an admixture of alkylene oxides containingethylene oxide and propylene oxide during at least 80% of the totaloxyalkylation in the presence of said double metal cyanide catalyst. 8.The polyoxypropylene polyol of claim 1 wherein the unsaturation of thepolyol is less than about 0.010 meq/g.
 9. A process for the preparationof a double metal cyanide catalyzed, high secondary hydroxyl grouppolyoxypropylene polyol by oxyalkylating one or more suitably hydricinitiator molecules with propylene oxide and optionally one or morehigher alkylene oxides to produce a high molecular weighttail-containing polyoxypropylene polyol having a decreased propensityfor phase-out during polyurethane formation, said processcomprising:oxyalkylating one or more suitably hydric initiator moleculeswith an alkylene oxide oxyalkylation mixture in the presence of aneffective amount of one or more double metal cyanide catalysts, whereinduring at least about 80 percent or more of said oxyalkylating, ethyleneoxide is present in said oxyalkylation mixture together with one or morehigher alkylene oxides such that oxyethylene moieties are present asrandom internal oxyethylene moieties in an amount of up to about 15weight percent of the polyoxypropylene polyol weight, and during aterminal portion of said oxyalkylating said oxyalkylation mixturecomprises substantially solely higher alkylene oxide, said oxyalkylationmixture during said terminal portion contributing not more than about 15weight percent of the total polyoxypropylene polyol weight; andrecovering a high secondary hydroxyl group-content low unsaturationpolyoxyalkylene polyol comprising a most major portion having anequivalent weight of between about 1000 Da and 15,000 Da, and a highmolecular weight polyoxyethylene/higher polyoxyalkylene polyether tailhaving a molecular weight greater than about 80,000 Da.
 10. The processof claim 9 wherein the unsaturation of the high secondary hydroxyl grouppolyoxypropylene polyol is less than about 0.010 meq/g.
 11. The processof claim 9 wherein the molecular weight of the high molecular weighttail is about 100,000 Da or more.
 12. The process of claim 9 wherein theweight percent ethylene oxide in said polyoxypropylene polyol is lessthan about 12% and the polyol contains a substantiallyhomopolyoxypropylene cap constituting from about 5 weight percent toabout 12.5 weight percent of said polyol weight.